How yeast sense direction in shallow pheromone gradients

这个项目将有助于我们理解梯度感应，细胞感知其表面化学浓度的微小差异，从而定位刺激源的能力。这种现象对所有生物体的发育和健康至关重要。主要研究者使用酵母细胞作为模型来研究梯度传感的分子机制，这被认为也广泛适用于更复杂的生物体中的细胞。在此项目期间，首席研究员和他的博士后科学家将指导从附近的马尔科姆X学院（MXC），芝加哥的城市学院之一，选择生物学学生，努力提高他们从四年制机构毕业的机会，在STEM领域的学士学位。拟议的本科研究和指导计划旨在激励，指导，建议和支持可能对STEM职业感兴趣的代表性不足的学生。调查还将通过与不同领域的专家合作者的互动，为学生和博士后科学家提供跨学科培训。由于该项目是在数学和生物学的接口，每个团队的研究人员将获得更好的理解所使用的方法，在其他学科。最著名的梯度刺激的细胞输出，趋化性（定向细胞运动）和趋化性（定向细胞生长），是需要广泛的生物过程。虽然它们最终表现出完全不同的行为，趋化性和趋化性细胞面临着类似的挑战：响应细胞必须感觉到其表面化学浓度的微小差异，确定梯度源的方向，并使其细胞骨架朝向它。酿酒酵母是趋化性的：交配细胞解释复杂的信息素梯度，并使它们的生长朝着最接近的伴侣的方向。像许多化学趋化细胞一样，酵母使用G蛋白偶联受体来检测潜在伴侣分泌的交配信息素，从而将它们的生长导向最近的信息素来源。这个项目的目标是了解趋化性生长位点是如何在细胞骨架极化之前建立的，以及细胞如何响应梯度方向的变化。已经提出了各种模型来解释酵母如何解释浅信息素梯度在体内，但没有令人满意地回答了基本的和长期存在的问题：细胞如何从默认的极性网站，他们用于细胞分裂，以建立一个趋化性网站，尽管接近零的信噪比开关？基于在以前的一个项目中的发现，首席研究员提出了一个回答这个问题的模型。工作假设是，交配酵母最初忽略信息素梯度，因为它们首先在默认位点共定位并集中信号和运输蛋白，构建“梯度跟踪机”（GTM）。一旦组装，GTM就沿着质膜移动到最大信息素浓度的点，在那里它标记了向化位点。本研究的重点是了解GTM是如何组装的，它如何移动到向化性位点，以及它如何引导向化性生长以响应梯度方向的变化。这些问题将使用成像，遗传学，光遗传学，生物化学和计算方法来回答，从而更深入地了解化学梯度传感。由于很少有人知道梯度排列的细胞极性是如何建立在其他真核生物的趋化性反应，一般原则可能会出现，将广泛影响趋化性现象的研究。此外，在这项调查中提出的许多问题都与其他跨膜信号系统有关，调查结果预计将揭示普遍相关的mechanism.This奖项反映了NSF的法定使命，并已被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。

This project will contribute to our understanding of gradient sensing, the ability of cells to sense small differences in chemical concentration across their surfaces, and thereby locate the source of the stimulus. This phenomenon is essential for the development and health of all organisms. The principal investigator uses yeast cells as a model to study the molecular mechanisms underlying gradient sensing, which are thought to be broadly applicable to cells in more complex organisms as well. During this project period, the principal investigator and his postdoctoral scientist will mentor select biology students from nearby Malcolm X College (MXC), one of the City Colleges of Chicago, in an effort to enhance their chances of graduating from a four-year institution with a BS in a STEM field. The proposed undergraduate research and mentoring program is designed to inspire, instruct, advise, and support underrepresented students who may be interested in a STEM career. The investigation will also provide students and the postdoctoral scientist with interdisciplinary training through interactions with collaborators who are experts in diverse areas. Because the project is at the interface of math and biology, researchers on each team will gain a better understanding of the methods used by those in the other discipline.The best-known gradient-stimulated cellular outputs, chemotaxis (directed cell movement), and chemotropism (directed cell growth), are required for a wide range of biologic processes. Although they ultimately exhibit quite different behavior, chemotactic and chemotropic cells face similar challenges: the responding cell must sense small differences in chemical concentration across its surface, determine the direction of the gradient source, and polarize its cytoskeleton toward it. The mating response of the budding yeast S. cerevisiae is chemotropic: mating cells interpret complex pheromone gradients and polarize their growth in the direction of the closest partner. Like many chemotaxing cells, yeast use G protein-coupled receptors to detect mating pheromone secreted by potential partners and thereby direct their growth toward the nearest pheromone source. The goal of this project is to understand how the chemotropic growth site is established before polarization of the cytoskeleton, and how the cell responds to changes in gradient direction. Various models have been proposed to explain how yeast interpret shallow pheromone gradients in vivo, but none satisfactorily answers the fundamental and long-standing question: how do the cells switch from the default polarity site they use for cell division to establish a chemotropic site, despite a near zero signal-to-noise ratio? Based on discoveries made during a previous project, the principal investigator proposed a model that answers this question. The working hypothesis is that mating yeast initially ignore the pheromone gradient, as they first colocalize and concentrate signaling and trafficking proteins at the default site, building a "gradient tracking machine" (GTM). Once assembled, the GTM moves along the plasma membrane to the point of maximal pheromone concentration, where it marks the chemotropic site. The priorities of this investigation are to learn how the GTM is assembled, how it moves to the chemotropic site, and how it steers chemotropic growth in response to changes in gradient direction. These questions will be answered using imaging, genetic, optogenetic, biochemical, and computational approaches, leading to a deeper understanding of chemical gradient sensing. Because little is known about how gradient-aligned cell polarity is established during the chemotropic responses of other eukaryotes, general principles are likely to emerge that will broadly influence the study of chemotropic phenomena. Moreover, many of the questions posed in this investigation are pertinent to other transmembrane signaling systems, and the findings are expected to reveal generally relevant mechanisms.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.